1. Field of the Invention
The present invention relates to an ignition device for igniting a foil cartridge in a power tool and, in particular, in a setting tool for driving in fastening elements such as nails, bolts and the like.
2. Description of the Prior Art
German Publication DE-199 05 549 A1 discloses an ignition device for igniting foil cartridges in an explosive powder charge-operated setting tool for driving in fastening elements. The ignition device includes a support, an electrical insulator arranged in the support, a pin-shaped electrode located in the electrical insulator and having a tip that communicates with surrounding environment via a channel formed in the electrical insulator and extending in a longitudinal direction of the pin-shaped electrode. The electrical insulator is pressed during a setting process against an electrically conducting foil that forms a bottom of a foil cartridge. The electrical arc, which is formed in the insulator channel melts the foil, which leads to ignition of a propellant contained in the cartridge.
The electrically conducting foil, which forms the cover strip of the foil cartridge, is formed by aluminum and has only a small durability. In addition, as a result of burning of aluminum, Al2O3 is formed.
However, the presence of Al2O3 in the power tools of this type is undesirable. Moreover, the insulator is mechanically not sufficiently rigid, and there is a danger of the central electrode being thrown out from the insulator upon build-up of high pressure resulting from the ignition of the cartridge. Furthermore, there exists a danger that hot, prestressed gases would flow through a gap between the electrode and the insulator and could cause further damage.
Accordingly, an object of the present invention is to provide an ignition device of the type described above and which has a mechanically rigid and reliable stricture.
Another object of the present invention is to provide an ignition device of the type described above and which would not require presence of electrically conducting elements on the foil cartridge.